import java.util.Scanner;

public class SequenceSum {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        long sum = 0;
        for (int i = 1 ; i <= n ; i++){
            sum += i;
        }
        System.out.println(sum);
    }
}
